Drilling system and method

A drilling system for drilling a bore hole into an earth formation, the bore hole having an inside wall, and the system comprising:

• a drill string reaching into the bore hole leaving a drilling fluid return passage between the drill string and the bore hole inside wall;
• a drilling fluid discharge conduit in fluid communication with the drilling fluid return passage;
• pump means for pumping a drilling fluid through the drill string into the bore hole and to the drilling fluid discharge conduit via the drilling fluid return passage;
• a bottom hole assembly supported by the drill string, the bottom hole assembly comprising a down hole sensor and a down hole telemetry system for transmitting data, including down hole sensor data, the down hole sensor data at least representing down hole pressure data;
• back pressure means controlling the drilling fluid back pressure;
• back pressure control means controlling the back pressure means, wherein the back pressure control means comprises a programmable pressure monitoring and control system arranged to receive the down hole sensor data, calculate a predicted down hole pressure using a model, compare the predicted down hole pressure to a desired down hole pressure, and to utilize the differential between the calculated and desired pressures to control said fluid back pressure means, and wherein the programmable pressure monitoring and control system is arranged to compare the predicted down hole pressure with the down hole sensor data.

A method of drilling a bore hole into an earth formation, the bore hole having an inside wall, the drilling method comprising the steps of:

• deploying a drill string from a surface into the bore hole and forming a drilling fluid return passage between the drill string and the bore hole inside wall, the drill string supporting a bottom hole assembly;
• pumping a drilling fluid through the drill string into the bore hole and via the drilling fluid return passage to a drilling fluid discharge conduit arranged in fluid communication with the drilling fluid return passage;
• obtaining information on the existing down hole pressure of the drilling fluid in the vicinity of the bottom hole assembly;
• feeding the information of the existing down hole pressure into a model;
• calculating a predicted down hole pressure using the model;
• comparing the predicted down hole pressure to a desired down hole pressure;
• controlling a drilling fluid back pressure by controlling back pressure means utilizing the differential between the calculated and desired pressures to control said fluid back pressure means.